Time-of-flight static secondary ion mass spectrometry of additives on polymer surfaces

A comparison of a polyethylene additive extract sample, deposited from solution as a submonolayer on Ag, was made to an in situ surface analysis of a bulk polyethylene sample using time-of-flight static secondary ion mass spectrometry (TOF-SIMS). The in situ analysis was able to confirm most of the additives detected in the extract. The additive mass range of 200–1200 Daltons was relatively free of spectral interferences due to the polyethylene matrix. High mass resolution studies were used to assist in the assignment of molecular identities to the additives. Molecular ions for the additives were predominantly Ag cationized adducts for the extract sample, and [M+H]+ or [M+Na]+ species for the bulk polyethylene. Deposition of standard additive solutions on Ag demonstrated the detection sensitivity of TOF-SIMS, illustrating the potential for molecular imaging of polymer domains as small as a few μm2 . The relative extent of oxidation of Naugard 524, an antioxidant additive, also was compared for a standard, polyethylene extract, and an in situ analysis using the [M+O]+ and [M+H]+ secondary ion signals. The additive was more extensively oxidized after aging in the polymer matrix based upon measurements of [M+H]+ /[M+O]+ ratios.